US8873138B2 - Auto focusing devices for optical microscopes - Google Patents

Auto focusing devices for optical microscopes Download PDF

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US8873138B2
US8873138B2 US13/608,404 US201213608404A US8873138B2 US 8873138 B2 US8873138 B2 US 8873138B2 US 201213608404 A US201213608404 A US 201213608404A US 8873138 B2 US8873138 B2 US 8873138B2
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light
specimen
light receiving
focus
optical microscope
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US20130070334A1 (en
Inventor
Kwang Soo Kim
Chang Hoon CHOI
In ho Seo
Hyun Jae Lee
Myoung Ki AHN
Byeong Hwan Jeon
Sung Jin Lee
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Samsung Electronics Co Ltd
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Samsung Electronics Co Ltd
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Assigned to SAMSUNG ELECTRONICS CO., LTD. reassignment SAMSUNG ELECTRONICS CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SEO, IN HO, CHOI, CHANG HOON, JEON, BYEONG HWAN, LEE, SUNG JIN, AHN, MYOUNG KI, KIM, KWANG SOO, LEE, HYUN JAE
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/28—Systems for automatic generation of focusing signals
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B21/00—Microscopes
    • G02B21/24—Base structure
    • G02B21/241—Devices for focusing
    • G02B21/245—Devices for focusing using auxiliary sources, detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/04—Measuring microscopes
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
    • G01N21/956—Inspecting patterns on the surface of objects
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/106—Beam splitting or combining systems for splitting or combining a plurality of identical beams or images, e.g. image replication
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/14—Beam splitting or combining systems operating by reflection only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
    • G02B7/28—Systems for automatic generation of focusing signals
    • G02B7/36—Systems for automatic generation of focusing signals using image sharpness techniques, e.g. image processing techniques for generating autofocus signals
    • G02B7/38—Systems for automatic generation of focusing signals using image sharpness techniques, e.g. image processing techniques for generating autofocus signals measured at different points on the optical axis, e.g. focussing on two or more planes and comparing image data

Definitions

  • Example embodiments may relate to focusing devices that may adjust focus of optical microscopes using laser scanning.
  • Example embodiments may relate to focusing devices that may automatically adjust focus of optical microscopes using laser scanning.
  • a semiconductor device is manufactured by repeatedly performing unit processes such as deposition, photolithography, etching, cleaning, testing, etc., on a surface of a wafer made of a semiconductor material such as silicon. Recently, there is a demand for high integration and high performance of the semiconductor device. To this end, individual semiconductor-manufacturing unit processes must be developed to enable a semiconductor device to have a fine feature size and high performance while maintaining a yield of the semiconductor device.
  • the defects may include scratches and/or particles formed at a thin film on the wafer, excessively-removed portions or non-removed portions of the thin film on the wafer, and/or pitting formed at the surface of the wafer, or the like.
  • the integration of the semiconductor device becomes higher, even micro-defects may lead to a serious malfunction of the semiconductor device, which otherwise and previously, may not adversely affect an operation or function of the semiconductor device. For this reason, there exists a need not only to reduce the defects formed in manufacturing the semiconductor device, but also to rapidly and accurately measure and test the defects formed on/at the wafer at a test process after each of the unit processes has been finished.
  • Image information acquired by an optical microscope, etc. may be used to detect the defects formed in manufacturing the semiconductor device or flat panel display (FPD).
  • the image information must have a high magnification and high resolution in order to improve the accuracy of the defect detection. It may be important to acquire clear image information of a pattern of a substrate (for example, the wafer or liquid crystal display (LCD) panel) by accurately detecting a focal point of the optical microscope. Moreover, a fast focus detection and/or adjustment may be required to be suitable for a fast test process.
  • Example embodiments may provide focusing devices for optical microscopes capable of laser-scanning an entirety of specimens to be tested using a wedge mirror.
  • Example embodiments may provide focusing devices that may automatically adjust focus.
  • Example embodiments may provide accurate movement of a specimen and/or objective lens to a focal point.
  • Example embodiments may provide a rotatable wedge mirror.
  • Example embodiments may provide focusing devices for optical microscopes capable of accurately moving a specimen and/or objective lens to a focal point when measuring and testing the specimen (for example, an LCD panel) made of a transparent material and having a small thickness, by using a confocal-type light receiving unit added to the focusing device for optical microscopes using laser scanning.
  • Example embodiments may provide focusing devices for optical microscopes capable of shortening focus adjustment durations (or improving focusing speeds) by using a combination of laser scanning and confocal-type mechanism, compared to the case when using only the confocal-type mechanism.
  • a focusing device for an optical microscope may include a light emitting unit configured to emit laser light having a specific wavelength; a wedge mirror configured to enable the emitted laser light to be incident on a plurality of locations of a surface of a specimen; first and second light receiving units configured to detect an amount of laser light reflected from the surface of the specimen; a spatial filter configured to eliminate out-of-focus light from light beams reflected from the surface of the specimen and to detect an amount of in-focus light; and/or a control unit configured to generate a control signal used to carry out focus adjustment of the optical microscope using a plurality of light-amount information detected by the first and second light receiving units and the spatial filter.
  • the spatial filter may include a light splitter configured to transmit some light reflected from the surface of the specimen and to reflect a remainder of the light reflected from the surface of the specimen; a pin hole member having a pin hole formed in the pin hole member; a condenser lens on an optical path between the light splitter and the pin hole member, the condenser lens configured to condense the light reflected from the light splitter to the pin hole so that the in-focus light is extracted; and/or a third light receiving unit configured to detect an amount of light incident on the third light receiving unit through the pin hole.
  • the light emitting unit may include a laser diode.
  • the focusing device may further include a collimating lens configured to enable beams of light emitted from the light emitting unit to be parallel to each other.
  • the focusing device may further include a half mirror between the wedge mirror and the collimating lens.
  • the half mirror may be configured to transmit some light passing through the collimating lens and incident on the half mirror; transmit some light reflected from the wedge mirror and incident on the half mirror; reflect a remainder of the light passing through the collimating lens and incident on the half mirror; and/or reflect a remainder of the light reflected from the wedge mirror and incident on the half mirror.
  • each of the first, second, and third light receiving units may include a photodiode.
  • control unit may be configured to carry out focus adjustment of the optical microscope by moving the specimen, an objective lens of the optical microscope, or an entirety of the optical microscope in an optical axis direction.
  • the focusing device may further include an actuator driver configured to receive the control signal from the control unit and to control, in response to the control signal, an operation of an actuator coupled to the specimen, the objective lens, or a body of the optical microscope so as to move the specimen, the objective lens of the optical microscope, or the entirety of the optical microscope in the optical axis direction.
  • an actuator driver configured to receive the control signal from the control unit and to control, in response to the control signal, an operation of an actuator coupled to the specimen, the objective lens, or a body of the optical microscope so as to move the specimen, the objective lens of the optical microscope, or the entirety of the optical microscope in the optical axis direction.
  • the control unit may be configured to determine a movement direction of the specimen, the objective lens, or the entirety of the optical microscope to achieve a focus match based on the calculated focus error value.
  • control unit may be configured to receive light-amount information from the third light receiving unit while moving the specimen, the objective lens, or the entirety of the optical microscope in the determined movement direction, and wherein when the specimen, the objective lens, or the entirety of the optical microscope reaches a position in the optical axis direction corresponding to a peak of the light-amount information received from the third light receiving unit, the control unit may be configured to stop the specimen, the objective lens, or the entirety of the optical microscope.
  • control unit may be configured to rotate so as to enable the emitted laser light to be incident on the plurality of locations of the surface of the specimen.
  • control unit may be configured to carry out focus adjustment of the optical microscope by moving the specimen, an objective lens of the optical microscope, or an entirety of the optical microscope in an optical axis direction.
  • the focusing device may further include an actuator driver configured to receive the control signal from the control unit and to control, in response to the control signal, an operation of an actuator coupled to the specimen, the objective lens, or a body of the optical microscope so as to move the specimen, the objective lens of the optical microscope, or the entirety of the optical microscope in the optical axis direction.
  • an actuator driver configured to receive the control signal from the control unit and to control, in response to the control signal, an operation of an actuator coupled to the specimen, the objective lens, or a body of the optical microscope so as to move the specimen, the objective lens of the optical microscope, or the entirety of the optical microscope in the optical axis direction.
  • one or both of the first and second light receiving units may include a photodiode.
  • the third light receiving unit may include a photodiode.
  • a focusing device for an optical microscope may include a light emitting unit; a half mirror; a wedge mirror; first and second light receiving units; and/or a control unit.
  • the light emitting unit may be configured to emit laser light having a specific wavelength.
  • the wedge mirror may be configured to enable the emitted laser light to be incident on a specimen.
  • the half mirror may be configured to transmit some light reflected from the wedge mirror and incident on the half mirror, and/or to reflect a remainder of the light reflected from the wedge mirror and incident on the half mirror.
  • the first and second light receiving units may be configured to detect an amount of laser light reflected from the specimen.
  • the control unit may be configured to carry out focus adjustment of the optical microscope using light-amount information detected by the first and second light receiving units.
  • the focusing device may further include a collimating lens configured to enable beams of light emitted from the light emitting unit to be parallel to each other.
  • the half mirror may be further configured to transmit some light passing through the collimating lens and incident on the half mirror, and/or to reflect a remainder of the light passing through the collimating lens and incident on the half mirror.
  • the focusing device may further include a light splitter configured to direct light from the half mirror to the first and second light receiving units.
  • the focusing device may further include a first condenser lens on an optical path between the light splitter and the first light receiving unit; and/or a second condenser lens on an optical path between the light splitter and the second light receiving unit.
  • FIG. 1 illustrates an optical system configuration of a focus detection unit in an auto focusing device for an optical microscope using laser scanning
  • FIG. 2 illustrates an equivalent model of light receiving units in the focus detection unit and a focal point when measuring and testing a specimen made of opaque material
  • FIG. 3 is a graph illustrating a relationship between a focus error (FE) and a focal point displacement using light-amount detection signals from the light receiving units in the focus detection unit;
  • FE focus error
  • FIG. 4 is a graph illustrating how to determine focus match or mismatch using light-amount detection signals from the light receiving units in the focus detection unit;
  • FIG. 5 illustrates an equivalent model of the light receiving units in the focus detection unit and a focal point when measuring and testing a specimen made of transparent material
  • FIG. 6 is a graph illustrating a relationship between a focus error (FE) and a focal point displacement using light-amount detection signals from the light receiving units in the focus detection unit when measuring and testing a specimen made of transparent material;
  • FE focus error
  • FIG. 7 illustrates an optical system configuration of a focus detection unit in a focusing device for an optical microscope according to some embodiments
  • FIG. 8 is a graph illustrating a waveform of a light-amount detection signal obtained by a confocal-type light receiving unit when measuring and testing a specimen made of transparent material;
  • FIG. 9 is a graph illustrating how to adjust a focus using the focusing device for the optical microscope according to some example embodiments.
  • FIG. 10 is a block diagram of controlling a focusing device for an optical microscope according to some example embodiments.
  • FIG. 11 is a flow chart of a focusing method using a focusing device for an optical microscope according to some example embodiments.
  • first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, and/or section from another element, component, region, layer, and/or section. For example, a first element, component, region, layer, and/or section could be termed a second element, component, region, layer, and/or section without departing from the teachings of example embodiments.
  • FIG. 1 illustrates an optical system configuration of a focus detection unit in an auto focusing device for an optical microscope using laser scanning.
  • FIG. 1 illustrates an optical system configuration of the optical microscope 100 and an optical system configuration of the focus detection unit 210 in an auto focusing device for the optical microscope 100 using laser scanning.
  • the optical microscope 100 generally includes an objective lens 110 , a light splitter 122 , a condenser lens 124 , a camera 130 , and/or an illumination unit (not shown).
  • the configuration of the illumination unit is not shown in order to focus on the configuration of the focus detection unit 210 .
  • the objective lens 110 receives light reflected from a specimen 10 .
  • a ratio of focal lengths between the objective lens 110 and the condenser lens 124 may determine a magnification.
  • the light splitter 122 receives light from the focus detection unit 210 and transfers the same to the specimen 10 .
  • the condenser lens 124 serves to condense light passing through the objective lens 110 and incident thereon to a sensor unit (not shown) of the camera 130 , so that an image of the specimen 10 is formed on the sensor unit of the camera 130 .
  • the camera 130 converts image information of the specimen 10 formed on the sensor unit thereof into an electrical signal which in turn is displayed through an image output device.
  • the camera may employ a charge-coupled device (CCD) sensor, a complimentary metal-oxide-semiconductor (CMOS) sensor, or the like.
  • CCD charge-coupled device
  • CMOS complimentary metal-oxide-semiconductor
  • the focus detection unit 210 in the auto focusing device for the optical microscope 100 using laser scanning may include a light emitting unit 212 , a collimating lens 214 , a half mirror 216 , a wedge mirror 218 , a light splitter 220 , a first condenser lens 222 , a second condenser lens 224 , a first light receiving unit 226 , and/or a second light receiving unit 228 .
  • the light emitting unit 212 emits light having a specific wavelength and may employ a laser diode (LD). However, example embodiments are not limited to laser diodes. Any device may be employed as the light emitting unit as long as the device emits light of a single color.
  • LD laser diode
  • the collimating lens 214 may cause beams of light emitted from the light emitting unit 212 to be parallel with each other.
  • the half mirror 216 transmits some of light passing through the collimating lens 214 and incident thereon and reflects the remainder of light passing through the collimating lens 214 and incident thereon.
  • the half mirror 216 transmits some of light reflected from the wedge mirror 218 and incident thereon and reflects the remainder of light reflected from the wedge mirror 218 and incident thereon.
  • the wedge mirror 218 reflects laser light emitted from the light emitting unit 212 so as to be incident upon the optical microscope 100 and again reflects light reflected from the light splitter 122 of the optical microscope 100 so as to be incident upon the half mirror 216 .
  • the light splitter 220 transmits some of light reflected from the wedge mirror 218 and half mirror 216 and incident thereon so as to be incident upon the first light receiving unit 226 .
  • the light splitter 220 reflects the remainder of light reflected from the wedge mirror 218 and half mirror 216 and incident thereon so as to be incident upon the second light receiving unit 228 .
  • the first condenser lens 222 condenses light passing through the light splitter 220 and incident thereon to one point of the first light receiving unit 226 .
  • the second condenser lens 224 condenses light reflected from the light splitter 220 and incident thereon to one point of the second light receiving unit 228 .
  • the first and second light receiving units 226 and 228 detect the amount of laser light which is emitted from the light emitting unit 212 and then reaches and reflects from the specimen 10 .
  • the first and second light receiving units 226 and 228 may employ photo diodes (PD).
  • PD photo diodes
  • example embodiments are not limited to photo diodes. Any device, including an avalanche photo diode (APD) or a photo multiplier tube (PMT), may be employed as the light receiving unit as long as the device receives light and detects the amount of the light.
  • APD avalanche photo diode
  • PMT photo multiplier tube
  • focus match a situation in which a focal point is formed exactly at the specimen
  • focus mismatch a situation in which a focal point is not formed exactly at the specimen
  • the focus match or mismatch may be determined based on amounts of reflected light detected by the first and second light receiving units 226 and 228 . This will be described in detail with reference to FIG. 3 and FIG. 4 .
  • laser light emitted from the light emitting unit 212 is reflected by the wedge mirror 218 (that may be rotatable) so as to be incident upon the optical microscope 100 . Then, light reflects from the light splitter 122 of the optical microscope 100 and then passes through the objective lens 110 and reaches and reflects from the surface of the specimen 10 . Light reflected from the surface of the specimen 10 again passes through the objective lens 110 and then reflects from the light splitter 122 and then again reflects from the wedge mirror 218 . Light reflected from the wedge mirror 218 reflects from the half mirror 216 and is incident upon the first and second light receiving units 226 and 228 .
  • the focus match or mismatch may be determined by analyzing amounts of light incident upon the first and second light receiving units 226 and 228 .
  • the first and second light receiving units 226 and 228 are displaced by a distance d from focal points formed by the first and second condenser lenses 222 and 224 respectively. That is, as shown in FIG. 1 , the first light receiving unit 226 is displaced forward by the distance d from a focal point formed by the first condenser lens while the second light receiving unit 228 is displaced backward by the distance d from a focal point formed by the second condenser lens.
  • the focal points formed by the first and second condenser lenses 222 and 224 respectively are distant by exactly the same distance from the first and second light receiving units 226 and 228 respectively.
  • the amount of light detected by the first light receiving unit 226 is equal to the amount of light detected by the second light receiving unit 228 .
  • FIG. 2 illustrates an equivalent model of the light receiving units in the focus detection unit and a focal point when measuring and testing the specimen made of an opaque material.
  • the focal points of laser light formed by the first and second condenser lenses 222 and 224 respectively are positioned by exactly the same distance from the first and second light receiving units 226 and 228 respectively.
  • this will be equivalent to the model shown in FIG. 2 .
  • a combination of the focus detection unit 210 and a portion of the optical microscope 100 shown in FIG. 1 may be equivalent to a model shown in FIG. 2 where laser light which reaches the specimen 10 and reflects from the surface of the specimen 10 and passes through the objective lens 110 is condensed by a condenser lens 223 so that a focal point FP of laser light is formed at an exactly central position between the first and second light receiving units 226 and 228 .
  • FIG. 3 is a graph illustrating a relationship between a focus error (FE) and a focal point displacement using light-amount detection signals from the light receiving units in the focus detection unit.
  • FE focus error
  • a solid line indicates a focus error signal.
  • the above equation 1 means the difference in detected light amount between the first and second light receiving units 226 and 228 .
  • the difference is divided by the sum of the detected light amounts of the first and second light receiving units 226 and 228 .
  • FIG. 3 and FIG. 4 there will be described how to determine focus match or mismatch using amounts of reflected light detected by the first and second light receiving units 226 and 228 .
  • focus adjustment is carried out using a left curve pattern with regard to a focus F in a graph of FIG. 3 .
  • a displacement when a focal point of laser light is formed at the specimen 10 becomes approximately 14.
  • the displacement or position of the specimen 10 is lower than the displacement or position of the specimen 10 when the focal point of laser light is exactly formed at the specimen 10 .
  • the specimen 10 is located below a position or displacement of the focus F. Accordingly, to carry out the focus adjustment using the left curve pattern with regard to the focus F in the graph of FIG. 3 may mean to carry out the focus adjustment while moving the specimen upwards.
  • the amount (PD 2 ) of reflected light detected by the second light receiving unit 228 is equal to the amount (PD 1 ) of reflected light detected by the first light receiving unit 226 , that is, the focus error (FE) value is zero, it is determined that the specimen 10 is located exactly at the focus F of laser light, that is, a focus match is achieved.
  • focus adjustment is carried out using a right curve pattern with regard to the focus F in the graph of FIG. 3 .
  • a displacement when a focal point of laser light is formed at the specimen 10 becomes approximately 14.
  • the position or displacement of the specimen 10 is higher than the position or displacement of the specimen 10 when the focal point of laser light is exactly formed at the specimen 10 .
  • the specimen 10 is located above a position or displacement of the focus F. Accordingly, to carry out the focus adjustment using the right curve pattern with regard to the focus F in the graph of FIG. 3 may mean carrying out focus adjustment while moving the specimen downwards.
  • the focus adjustment may be carried out rapidly and accurately by using the focusing device for the optical microscope using laser scanning as described above with reference to FIG. 1 to FIG. 4 .
  • the focus adjustment is carried out by using the focusing device for the optical microscope using laser scanning as described above in measuring and testing the specimen (for example, an LCD panel) made of a transparent material and having a small thickness (for example, 450 ⁇ m or 700 ⁇ m), an unclear focal point is formed during focus adjustment of the optical microscope using the objective lens 110 having a specific magnification (for example, equal to or smaller than 10 ).
  • laser light reflects from upper and lower surfaces of the transparent specimen 10 and then both of a light beam reflected from the upper surface and a light beam reflected from the lower surface are incident upon the first and second light receiving units 226 and 228 , so that two focal points of the laser light are formed by the first and second condenser lenses 222 and 224 and are positioned between the first and second light receiving units 226 and 228 .
  • FIG. 5 illustrates an equivalent model of the light receiving units in the focus detection unit and a focal point when measuring and testing the specimen made of a transparent material.
  • FIG. 5 illustrates how two respective focal points for the light beam reflected from the upper surface of the specimen 10 and the light beam reflected from the lower surface of the specimen 10 are formed near the first and second light receiving units 226 and 228 .
  • a solid line indicates the laser light beam reflected from the upper surface of the transparent specimen 10
  • a dotted line indicates the laser light beam reflected from the lower surface of the transparent specimen 10 .
  • the two respective focal points F 1 and F 2 for the two beams of reflected light are formed by the condenser lens 223 and are positioned between the first and second light receiving units 226 and 228 .
  • the amount (PD 1 ) of reflected light detected by the first light receiving unit 226 is equal to the amount (PD 2 ) of reflected light detected by the second light receiving unit 228 because the focal point F 1 for light reflected from the upper surface of the transparent specimen 10 is formed at a central position between the first and second light receiving units 226 and 228 .
  • the focal point F 2 for light reflected from the lower surface of the transparent specimen 10 is formed near the first light receiving unit 226 as shown in FIG. 5 , the amount (PD 1 ) of reflected light detected by the first light receiving unit 226 is not equal to the amount (PD 2 ) of reflected light detected by the second light receiving unit 228 .
  • FIG. 6 is a graph illustrating a relationship between a focus error (FE) and a focal point displacement using light-amount detection signals from the light receiving units in the focus detection unit when measuring and testing the specimen made of a transparent material.
  • FE focus error
  • laser light reflects from upper and lower surfaces of the transparent specimen 10 and then both of the light beam reflected from the upper surface and the light beam reflected from the lower surface are incident on the first and second light receiving units 226 and 228 , so that the two focal points of the laser light are formed and positioned between the first and second light receiving units 226 and 228 . Therefore, there may occur a change in a signal waveform of a focus error FE calculated using amount (PD 1 ) of reflected light detected by the first light receiving unit 226 and amount (PD 2 ) of reflected light detected by the second light receiving unit 228 .
  • a solid line indicates a signal waveform of a focus error FE obtained when measuring and testing the specimen 10 made of an opaque material
  • a dotted line indicates a signal waveform of a focus error FE obtained when measuring and testing the specimen 10 made of a transparent material.
  • the focusing device for the optical microscope using laser scanning further includes a confocal-type light receiving mechanism.
  • a confocal-type light receiving mechanism In this way, when measuring and testing the specimen made of a transparent material and having a small thickness, it may be possible to carry out the focus adjustment by accurately moving the specimen and/or objective lens to achieve a focus match.
  • FIG. 7 illustrates an optical system configuration of a focus detection unit in a focusing device for an optical microscope according to some example embodiments.
  • FIG. 8 is a graph illustrating a waveform of a light-amount detection signal obtained by the confocal-type light emitting mechanism when measuring and testing the specimen made of a transparent material.
  • each of other components than the confocal-type light receiving mechanism may have the same configuration as in the optical system configuration of the focus detection unit in the focusing device for the optical microscope using laser scanning as shown in FIG. 1 . Therefore, only a configuration of the confocal-type light receiving mechanism will be described in detail hereinafter.
  • the focus detection unit 210 in the focusing device for the optical microscope may further a spatial filter 230 between the half mirror 216 and light splitter 220 . That is, a confocal-type light receiving mechanism is added to the focusing device for the optical microscope using laser scanning.
  • the spatial filter refers to a spatial pin hole and serves to eliminate a light beam reflected from positions other than a focal point.
  • the confocal-type light receiving mechanism may mean that the out-of-focus light beam reflected from the specimen 10 is eliminated from the reflected laser light beams and only the in-focus light reflected from the specimen 10 is used, so that the light beam reflected from the upper surface of the transparent specimen 10 and the light beam reflected from the lower surface of the transparent specimen 10 are separated from each other.
  • the spatial filter 230 may include a light splitter 232 , a third condenser lens 234 , a pin hole member 236 having a pin hole P formed therein, and/or a third light receiving unit 238 .
  • the light splitter 232 transmits some of light reflected from the wedge mirror 218 and half mirror 216 and incident thereon so as to be incident on the light splitter 220 .
  • the light splitter 232 reflects the remainder of light reflected from the wedge mirror 218 and half mirror 216 and incident thereon so as to be incident on the third light receiving unit 238 .
  • the third condenser lens 234 condenses light reflected from the light splitter 232 to the pin hole P so that only in-focus light is extracted.
  • the third light receiving unit 238 detects the amount of light incident thereon through the pin hole P.
  • the third light receiving unit 238 may employ photo diodes (PD).
  • the confocal-type light receiving mechanism has a high sensitivity to a focal plane. Therefore, when laser scanning operation for the thin and transparent specimen is performed in an optical axis (Z axis) direction, a graph as shown in FIG. 8 may be obtained. Here, a position along the Z axis corresponding to a peak of a waveform of the light-amount detection signal from the third light receiving unit 238 as shown in FIG. 8 becomes a focal point.
  • a waveform of the light-amount detection signal for light reflected from the upper surface of the specimen 10 (as indicated by a solid line in FIG. 8 ) and a waveform of the light-amount detection signal for light reflected from the lower surface of the specimen 10 (as indicated by a dotted line in FIG. 8 ) have single peaks respectively.
  • focal points may be located.
  • both of light reflected from the upper surface of the specimen 10 and light reflected from the lower surface of the specimen 10 are incident on the first, second, and third light receiving units 226 , 228 , and 238 . Therefore, for the purpose of an accurate focus adjustment, it should be determined in advance which one of the upper and lower surfaces of the specimen 10 will be referenced when carrying out the focus adjustment.
  • the specimen 10 When carrying out focus adjustment using only the confocal-type mechanism instead of using a combination of laser scanning and confocal-type mechanism, the specimen 10 should be scanned along an entirety of the Z axis in order to locate the positions corresponding to the peaks of the light-amount detection signal. Moreover, when the specimen 10 is made of a transparent material, it is necessary to determine from which one of the upper and lower surfaces of the specimen 10 a light beam in question is reflected. For these reasons, when carrying out the focus adjustment using only the confocal-type mechanism, focus adjustment speed may be lower.
  • the focusing device for the optical microscope according to some example embodiments may use the combination of laser scanning and confocal-type mechanism. Therefore, the focusing device for the optical microscope according to some example embodiments may shorten the focus adjustment duration or improve the focus adjustment speed, compared to the case of carrying out focus adjustment using only the confocal-type mechanism.
  • the focus mismatch situation in which the specimen 10 is not positioned at the focal point it may be determined using a difference value (or focus error value) between amounts (PD 1 and PD 2 ) of reflected light detected by the first and second light receiving units 226 and 228 respectively whether to move the specimen 10 upwards or downwards to achieve the focus match.
  • a difference value or focus error value
  • the focus match of the optical microscope 100 may be achieved rapidly and accurately by moving the specimen 10 to the position in the optical axis corresponding to the peak of the waveform of the light-amount detection signal of light reflected from any selected one of the upper and lower surfaces of the specimen 10 using the confocal-type light receiving mechanism without the need to scan the specimen 10 along an entirety of the Z axis or optical axis.
  • FIG. 9 there will be described how to adjust a focus using the focusing device for the optical microscope according to some example embodiments.
  • the specimen 10 when measuring and testing the thin specimen 10 made of the transparent material, the specimen 10 may be brought exactly to the focal point by using a signal waveform of the focus error value obtained when measuring and testing the specimen 10 made of the transparent material (as indicated by a dotted line in FIG. 9 ) and a waveform of the light-amount detection signal (amount (PD 3 ) of reflected light detected by the third light receiving unit) from the confocal-type light receiving unit (as indicated by a solid line in FIG. 9 ).
  • a signal waveform of the focus error value obtained when measuring and testing the specimen 10 made of the transparent material as indicated by a dotted line in FIG. 9
  • a waveform of the light-amount detection signal asmount (PD 3 ) of reflected light detected by the third light receiving unit
  • the waveform of the focus error signal calculated from the amounts (PD 1 and PD 2 ) of reflected light detected by the first and second light receiving units 226 and 228 respectively (as indicated by a dotted line in FIG. 9 ) whether to move the specimen 10 upwards or downwards to achieve the focus match of the specimen 10 . That is, the upward or downward movement of the specimen 10 is determined. Further, when the specimen reaches, while moving the specimen 10 in the determined direction, the position in the optical axis corresponding to the peak of the waveform of the light-amount detection signal (PD 3 ) from the confocal-type light receiving unit (as indicated by a solid line in FIG. 9 ), the specimen 10 stops. That is, the focal point toward which the specimen 10 move is determined. In this way, the focus match of the optical microscope 100 is achieved.
  • a focus adjustment is carried out using the light-amount detection signal (PD 3 ) from the third light receiving unit ( 328 ) while moving the specimen upwards.
  • focus adjustment is carried out using the light-amount detection signal (PD 3 ) from the third light receiving unit ( 328 ) while moving the specimen downwards.
  • FIG. 10 is a block diagram of controlling a focusing device for an optical microscope according to some example embodiments.
  • the optical microscope 100 is constructed such that an objective lens 110 and barrel 120 are coupled to a camera 130 .
  • the barrel 120 there may be disposed the light splitter 122 , the condenser lens 124 , an illumination unit (not shown), etc.
  • the light splitter 122 , the condenser lens 124 , and the illumination unit are not shown in FIG. 10 .
  • a focusing device 200 configured to adjust a focus of the optical microscope 100 may be connected to the optical microscope 100 .
  • Focusing device 200 may be configured to automatically adjust a focus of the optical microscope 100 .
  • the focusing device 200 of the optical microscope 100 may include a focus detection unit 210 , a control unit 240 , and/or an actuator driver 250 .
  • the focus detection unit 210 detects a distance between the specimen 10 and the objective lens 110 and thus accurately locates the focal point.
  • the focus detection unit 210 may include the light emitting unit 212 to emit laser light having a specific wavelength and/or the first, second, and third light receiving units 226 , 228 , and 238 to detect amounts of laser light emitted from the light emitting unit 212 and reaching and reflected from the specimen 10 .
  • the third light receiving unit 238 as the confocal-type light receiving unit receives only the in-focus light beam among laser light beams reaching and reflected from the specimen 10 while the out-of-focus light beam is eliminated from the laser light beams reaching and reflected from the specimen 10 .
  • the control unit 240 controls operations of the focusing device 200 . To this end, the control unit 240 receives a plurality of the light-amount information (PD 1 , PD 2 and PD 3 ) from the first, second, and third light receiving units 226 , 228 , and 238 in the focus detection unit 210 respectively and generates a control signal used to carry out focus adjustment using the received light-amount information (PD 1 , PD 2 and PD 3 ).
  • the control unit 240 sends the control signal to the light emitting unit 212 so that the light emitting unit 212 emits laser light having a specific wavelength.
  • the control unit 240 receives light-amount information (PD 1 and PD 2 ) from the first and second light receiving units 226 and 228 and calculates the focus error (FE) value using the received light-amount information (PD 1 and PD 2 ).
  • the control unit 240 determines whether to move the specimen 10 upwards or downwards to archive the focus match, depending on whether the calculated focus error value is positive or negative.
  • the control unit 240 receives the light-amount detection signal (PD 3 ) from the confocal-type light receiving unit (i.e. the third light receiving unit ( 238 )) while moving the specimen 10 in the determined direction.
  • the control unit stops the specimen 10 . In this way, the focus match of the optical microscope 100 is achieved.
  • the control unit 240 generates a control signal used to carry out the focusing operation based on a plurality of the light-amount information (PD 1 , PD 2 and PD 3 ) received from the first, second, and third light receiving units 226 , 228 , and 238 .
  • the control signal may include information on the movement direction of the specimen 10 and timing when the specimen 10 stops.
  • the control unit 240 sends this control signal to the actuator driver 250 .
  • the control unit 240 may have a memory 240 a therein.
  • the memory 240 a to store the desired (or alternatively, predetermined) information necessary to carry out the focusing operation is provided within the control unit 240 .
  • example embodiments are not limited to storing the information in memory 240 a .
  • the desired (or alternatively, predetermined) information necessary to carry out the focusing operation may be stored in a separate storage unit instead of the internal type memory 240 a.
  • the actuator driver 250 controls an operation of an actuator (not shown) such as a motor or a piezoelectric device or the like coupled to a support (not shown) on which the specimen 10 is mounted so as to move the specimen 10 in the optical axis (Z axis) direction in response to the control signal received from the control unit 240 so that the specimen 10 reaches the focal point determined by the control unit 240 .
  • an actuator such as a motor or a piezoelectric device or the like coupled to a support (not shown) on which the specimen 10 is mounted so as to move the specimen 10 in the optical axis (Z axis) direction in response to the control signal received from the control unit 240 so that the specimen 10 reaches the focal point determined by the control unit 240 .
  • the specimen 10 moves in the optical axis (Z axis) direction to carry out the focus adjustment.
  • example embodiments are not limited to the specimen moving by itself. Not the specimen 10 but the objective lens 110 moves in the optical axis (Z axis) direction to carry out focus adjustment. Otherwise, an entirety of the barrel 120 moves in the optical axis (Z axis) direction to carry out focus adjustment.
  • FIG. 11 is a flow-chart of a focusing method using a focusing device for an optical microscope according to some example embodiments.
  • FE focus error
  • example embodiments are not limited to the specimen moving by itself. Instead of the specimen, the objective lens of the optical microscope or the entirety of the optical microscope may move in the optical axis direction.
  • the control unit 240 sends the control signal to the light emitting unit 212 so that the light emitting unit 212 emits laser light having a specific wavelength (operation 305 ). Laser light emitted from the light emitting unit 212 reaches and is reflected from the surfaces of the specimen 10 and returns to the focus detection unit 210 .
  • the control unit 240 receives, respectively, from the first and second light receiving units 226 and 228 the light-amount information (PD 1 and PD 2 ) of laser light reflected from the surfaces of the specimen 10 and incident on the first and second light receiving units 226 and 228 (operation 310 ).
  • the light-amount information (PD 1 and PD 2 ) of laser light received from the first and second light receiving units 226 and 228 is stored in the memory 240 a of the control unit 240 .
  • control unit 240 calculates the focus error (FE) value using the light-amount information (PD 1 and PD 2 ) of laser light received from the first and second light receiving units 226 and 228 (operation 315 ).
  • control unit 240 determines whether the calculated focus error (FE) value is greater than zero (operation 320 ).
  • the control unit 240 determines that the specimen 10 is located below the focal point and thus sends an associated control signal to the actuator driver 250 so that the actuator driver 250 moves the specimen 10 upwards.
  • the control unit 240 receives, while continuously moving the specimen 10 upwards, from the third light receiving unit 238 the light-amount information (PD 3 ) of laser light reflected from the surfaces of the specimen 10 and incident on the third light receiving unit 238 (operation 325 ).
  • the light-amount information (PD 3 ) input from the third light receiving unit 238 is stored in the memory 240 a of the control unit 240 .
  • the control unit 240 compares currently-input light-amount information (PD 3 ) with a maximum value of previously-input light-amount information (PD 3 ) and thus continuously updates the maximum value of light-amount information (PD 3 ) and then stores the undated maximum value of light-amount information (PD 3 ) in the memory 240 a .
  • the third light receiving unit 238 receives only the in-focus light beam among the laser light beams reaching and reflected from the specimen 10 while the out-of-focus light beam is eliminated from the laser light beams reaching and reflected from the specimen 10 .
  • the control unit 240 determines whether the light-amount information (PD 3 ) of the in-focus laser light detected by the third light receiving unit 238 reaches the peak (operation 330 ).
  • the control unit 240 determines that the moving specimen 10 reaches the focal point and then terminates the focusing operation. More specifically, when a result from subtracting currently-input light-amount information (PD 3 ) from the maximum value of previously-input light-amount information (PD 3 ) stored in the memory 240 a is above a preset value, the control unit 240 determines that the specimen just passed by the peak of the waveform of the light-amount information (PD 3 ) of light detected by the third light receiving unit 238 and is currently located at a falling point of the waveform. Accordingly, the control unit 240 moves the specimen 10 to the position in the optical axis corresponding to the peak of the waveform of the light-amount detection signal. In this way, the focus match of the optical microscope 100 is achieved.
  • the process returns to operation 325 in which the control unit 240 receives, while continuously moving the specimen 10 upwards, from the third light receiving unit 238 the light-amount information (PD 3 ) of reflected laser light.
  • control unit 240 determines whether the calculated focus error (FE) value is less than zero, that is, is a negative value (operation 335 ).
  • the control unit 240 Upon determining that the calculated focus error (FE) value is less than zero (“yes” in operation 335 ), the control unit 240 determines that the specimen 10 is located above the focal point and thus sends an associated control signal to the actuator driver 250 so that the actuator driver 250 moves the specimen 10 downwards. Then, the control unit 240 receives, while continuously moving the specimen 10 downwards, from the third light receiving unit 238 as the confocal-type light receiving unit the light-amount information (PD 3 ) of laser light reflected from the surfaces of the specimen 10 and incident on the third light receiving unit 238 (operation 340 ). The light-amount information (PD 3 ) input from the third light receiving unit 238 is stored in the memory 240 a of the control unit 240 . The control unit 240 again determines whether the light-amount information (PD 3 ) of the in-focus laser light detected by the third light receiving unit 238 reaches the peak (operation 345 ).
  • the control unit 240 determines that the moving specimen 10 reaches the focal point and then terminates the focusing operation.
  • the process returns to the operation 340 in which the control unit 240 receives, while continuously moving the specimen 10 downwards, from the third light receiving unit 238 the light-amount information (PD 3 ) of reflected laser light.
  • the control unit 240 may not determine whether the specimen 10 is located above or below the focal point. Therefore, the control unit 240 sends a control signal to the actuator driver 250 so that the specimen 10 moves in any selected one of the upward and downward directions.
  • the control unit 240 receives, while continuously moving the specimen 10 in any selected one of the upward and downward directions, from the third light receiving unit 238 the light-amount information (PD 3 ) of laser light reflected from the surfaces of the specimen 10 and incident on the third light receiving unit 238 (operation 350 ).
  • the control unit 240 Upon determining that the light-amount information (PD 3 ) input from the third light receiving unit 238 gradually decrease when moving the specimen 10 in any selected one of the upward and downward directions, the control unit 240 determines that the specimen 10 becomes gradually farther away from the focal point. Thus, the control unit 240 sends a control signal to the actuator driver 250 so that the specimen 10 moves in an opposite direction to the selected one of the upward and downward directions. The control unit 240 receives, while continuously moving the specimen 10 in the opposite direction, from the third light receiving unit 238 the light-amount information (PD 3 ) of laser light reflected from the surfaces of the specimen 10 and incident on the third light receiving unit 238 .
  • control unit 240 again determines whether the light-amount information (PD 3 ) of the in-focus laser light detected by the third light receiving unit 238 reaches the peak (operation 355 ).
  • the control unit 240 determines that the moving specimen 10 reaches the focal point and then terminates the focusing operation.
  • the process returns to the operation 350 in which the control unit 240 receives, while continuously moving the specimen 10 in any selected one of the upward and downward directions, from the third light receiving unit 238 , the light-amount information (PD 3 ) of reflected laser light.

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